The present disclosure relates generally to a method for cooling a data acquisition system (DAS) and detectors associated with computer assisted tomography (CAT) and in particular, to a method for cooling a DAS/detectors in different air temperatures and air flow rates using a variable speed fan to compensate for rotation of the gantry.
The present disclosure pertains to the art of medical diagnostic imaging and more particularly to computerized tomographic (CT) scanners. The disclosure finds particular application in conjunction with cooling systems associated with CT scanners and will be described with particular reference thereto. It will be appreciated, however, that the invention has broader applications and may be advantageously employed in other environments.
CT scanner cooling systems of the type to which this invention pertains have ordinarily included air conditioning units housed within CT scanner gantries. Such air conditioning units were deemed necessary because they cooled sensitive radiation detectors and other components associated with the CT scanners. When a CT scanner is in operation, an X-ray beam rotates rapidly in a patient examination region. A rotating anode X-ray tube rotates continuously around the examination region and causes the beam to so rotate. The X-ray anode generates a significant amount of heat as well as the X-rays. Because the radiation detectors lose linearity and fail prematurely when heated, they are kept cool. A typical CT scanner cooling system uses an air conditioned sealed gantry to maintain radiation detectors at a proper working temperature.
The use of air conditioning systems in connection with CT scanners has several drawbacks. First, the air conditioning units take up valuable space within the CT scanner gantry. The units are relatively cumbersome, and limit the amount of space available for the various CT scanner features.
Second, air conditioning units require frequent maintenance. If the air conditioning unit breaks down, the detectors can overheat during CT scanner use. Further, the air conditioning units are not readily removable. Their position within a CT scanners makes it difficult to repair other CT scanner parts and features by inhibiting free access to such parts.
Currently, data acquisition system (DAS) cooling is also done with constant speed fans which are always on. A current integrated DAS/detector design is extremely sensitive to cooling air temperature control, air flow rate and rapid changes in cooling air flow rate and temperature. The most sensitive and therefore potentially useful detectors for this application are solid state devices made up of a scintillating crystal for converting the x-ray energy to light and a semiconductor photo-diode to convert the light to an electrical signal that can be computer processed. Unfortunately, however, both of these devices are temperature sensitive, with the photo diode responding exponentially to temperature. Operation of the x-ray source and power supplies generates a large amount of heat that causes the ambient temperature inside the CT system to rise significantly. Changes in A/D card temperatures are directly reflected in the diode temperatures operably connected to the A/D card. Accurate temperature control or compensation for each of the solid state detectors is therefore an important requirement.
It is a very difficult design challenge to control the air temperature variation within a gantry and is subject to a multitude of design constraints such as, room air temperature control, allowable system packaging volume in an existing CT gantry platform (e.g., major components and component placement not easily changed or modified). Current CT systems have air temperature variations (e.g., 15° C.) which are unacceptable for current DAS/detector design. Control of the air temperature and flow rate due to gantry rotations is an even more challenging design issue and is not addressed by current system designs and expected to get worse as system rotational speeds increase. Furthermore, current DAS cooling fans are loud and barely meet audible specifications for such fans.
Accordingly, a method and system to quietly cool a DAS/detector is desired that limits an air temperature variation in the gantry on the order of less than 15° C. and maintains cooling fan efficiency as the fan is rotated when the gantry is rotated.